US501654A - Power-measuring instrument for steam-engines - Google Patents

Description

' (N man.) 5 sheetssheet 2j. W. '13. HoWARn.

POWER MEASURING INSTRUMENT FOR STEAM ENGINES. Y No. 501,654. Patented' July 18, 1893.

' Fig 2;

POWER MEASURING I IIIIIIIII III III-IIIIII IIIIIIIII I IIIIIIIII I W. T. HOWARD. I

NSVTRUMENT PORSTBAM ENGINES'.

Patented ZJ Y 5 Sheets-Sheet 3...

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(No Model.)

W. T. HOWARD. POWER MEASURING INSTRUMENT .FOR STEAM ENGINES.

PaAientedVJ'ulyl 18, 1893..

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-WITNEEEEE (No Model.) 5. sheets-sheet 5.

i w. T. HOWARD. POWER MEASURING INSTRUMENT FOR STEAMENGINES.

Patented July 18,11%?,9g3-11 .UNITED- STATES PATENT OFFICE.

WILLIAM THOMPSON HOWARD, OF BALTIMORE, MARYLAND.

POWER-MEASURING INSTRUMENT FOR STEAM-VENGINES.

' SPECIFICATION forming part ef Letters Patent Ive. 501,654, dated July 1e, 1893.

Application filed November 19, 18192. Serial No. 452,537. [No model.)

To all whom it may concern.-

Be it known that I, WILLIAM THOMPSON` HOWARD, of the city of Baltimore and State ot Maryland, have invented certain Improvements in Power-Measuring Instruments for Steam-Engines, of which the following is a specification.

This invention is based on the discovery which I have made, that the mean pressure of steam acting on the piston of a steam engine for a certain period of time may be accurately ascertained by computing or measuring the quantity orbulk of mercury forced or discharged througha small aperture by steam in communication with that acting on the piston,the capacity of discharge of the said aperture under various constant pressures for the same period oftime being known. The

time during which the steam is allowed to act.

on the body of mercury is not of vital importance. It may be a fraction of a minute, or two or more minutes; but as one minute is the unit of time used in computing horse power, thatA period is best suited for the purpose. One important advantage in extending the time to at leastone minute, is that a fair average mean pressure may be obtained; as, during that period, in nearly all cases, all the various operations of the machinery driven by the engine will ,have been performed. To apply this principle of ascertaining the mean pressure ofrsteam acting, on the piston of a non-condensing .steam engine, I employ, primarily, aV mercury-holding vessel having a small discharge aperture in communication with, or leading to,a measuring vessel, which for the sake of convenience4 consists ofaglass tube; and use in connection therewith, suitable valve mechanism whereby the steam from the two ends of the cylinder is alternately brought in communication with the said said mercury holding vessel, so as to act upon, the body of mercury in the said Vessel, and thereby force or discharge a portion of it to a mercury reservoir where it displaces a lighter liquid such as Water' or Water and glycerine suitably colored, resting on the mercury and forces it up the said measuring vessel or glass tube by which means the average pressure, acting on both sides of the piston during a double stroke or series of double strokes, is ascertained. I further employ in connection with the first body of mercury a second body, a reservoir and a meas tiring-glass tube, toy ascertain the retarding or back pressure on the piston; thev valve mechanism before alluded to being so arranged that the forward pressure in all cases acts on one body of mercury, while the retarding or back pressure act-s on the other. By this arrangement, I obtain two columns of mercury one representing the averageforward, and the other the average back, pressure; and bydeducting the figures indicating ythe latter from those representing the former, the mean effective pressure on the piston during the time to which the mercury is subvjected to the action of the steam, is accurately ascertained. But to make the columns of lmercury with their upper stratum of light liquid available for the purpose in view, itis -necessary that scales should be prepared whereby the quantity or bulk of vmercury discharged uuder various pressures may be readily computed; and to effect this, the bodies of mercury in the preparationV of the instrument for use are subjected to different constant pressures for the unit of time fined upon,one minute, and the heights attained by the columns of light liquid under the various constant pressures marked.

In practice, the operation of preparing the scales is as follows: Each body of mercury is subjected to a pressure of, say, five pounds, steam, air or water being used, for the space of one minute, and the height to which the ycolored column rises marked. The pressure is then removed and the mercury allowed to descend to its original height, which brings the surface of the colored liquid to its original level or the zero point, and a pressure ofsay 'ten pounds applied for the same period of time,

after which the column is again allowed to descend to the zero point. This operation is continued with a successive advance in pressure at each trial, of say ten pounds, until the maximum pressure is reached. Theten pound spaces are then divided into pound spaces or less, thus completing the scale.

It is found in practice that divisions of ten pounds, ascertained by actual pressures,

will give sufficient accuracy; but it is evident that every pound between the zero mark and the maximum pressure may be registered by IOO actual trial or subjecting the mercury to each diiierent pressure for the space of one minute.

In preparing the scale, a vertical scale line is drawn on a sheet of paper, and the heights of the pressure columns, ascertained as before d escribed, and which represent pressuresfrom, say, zero to eighty pounds marked thereon. From these points or marks are drawn horizontal lines, the first or zero line being the base. Y

The base line which may be of any convenientlength is then pointed off into eight equal spaces and perpendicular lines are erected from the division points, which are numbered to correspond with those on the scale line, or from zero to eighty. A curved line is then drawn through the points where the perpendicular and horizontal lines intersect which' curved line represents' in general outlinea parabolic curvo. The sub-divisions, to represent pounds, are then easily obtained by dividing the ten pound spaces on the base line into ten equal parts, and erecting perpendiculars from the points to intersect the parabolic curve, andextending horizontal lines from the intersecting points to the scale line.

In applying the invention to ascertain the horse power of condensing engines in which a portion of the pressure of the atmosphere is added to that of the steam acting on the engine piston, the colored liquid in the back pressure column will descend instead of ascending, and, to compute the proportion of theatmospheric pressure used, a second set of indicating numerals is marked on the back pressure scale, beginning at the zero point, the figures advancing in a downward direction. The pressure of the steam acting on the piston not being constant., it is evident that in the formation of a column the movement of the colored liquid in the glass tubes will vary, its speed of rise being faster at the beginning than at the termination of the stroke, but the bulk of mercury discharged with a varying pressure, the mean of which is, say, fifty pounds, will be the same as that discharged in the same time when, in forming the scale, a constant pressure of fifty pounds was used. For example, supposing the initial pressure on the piston to be one hundred pounds, and the steam cut off at one quarter of the stroke the terminal pressure will be about fourteen pounds, and the mean pressure about fiftyfour pounds. At the beginning ofthe stroke, the discharge of mercury will be at the same rate as that which in the formation of the scale carried the column to the one hundred pound mark. But as the piston advances, the rapidity of discharge will decrease until, at the termination of the stroke, it will be at the rate of that when the fourteen pound mark was ascertained. Hence the rapidity of discharge will average the fifty-four pound rate, and, at the termination of the minute, the

colored column will have reached the point' indicated by that number on the scale. While this result is being reached in the forward pressure tube, the average back pressure is recorded on the scale applied to the other; and it is evident that the value of the two records obtained by deducting the back pressure from the forward one is the mean effective pressure acting on the piston for the s pace of one minute from which, the arca and speed of piston being known, the horse power of the engine may be computed.

As the exact speed of the piston is a necessary element to be taken into consideration in computing the horse ,power of an engine,

y a secondary part of the invention consists in combining with the pressure-ascertaining devices before described, improved means whereby each complete or double stroke of the piston is registered, so that at the termination of the minute of trial, the aggregate number may be known, as will hereinafter appear.

In the further description of the invention which follows reference is made to the accompanying drawings forming a part hereof and in which` Figure l is a perspective view of a steam engine provided with the improved power measuring instrument, illustrating, principally, the means employed for communicating motion from the crosshead of the engine to the instrument. Fig. 2 is a front view of the instrument alone, certain parts thereof being removed to show the interior. Fig. 3 is an exterior side view of the invention. Fig. 4 is a plan of Fig. 2. Figs. 5 to 22, inclusive, are details of the instrument on an enlarged scale.

Referring to the drawings, A is the frame of the instrument, having at the bottom two hollow bosses d' and b. The boss ct is in communication with one end of the engine cylinder, and the boss b with the other end, the means of communication bei-ng the pipes c and d, and the coupling cocks e andf, shown in Fig l.

Referring more particularly to Figs. 2, 3 and 4 B and C are cylindrical steam holding vessels supported by the frame A, and situated over the hollow bosses a and b. Beneath the steam holding vessels B and C, is acharnber D. for the cylindrical reversing valve E, hereinafter described. The cylindrical chamber D is formed of a fixed sleeve D2 and has ports g, h, e', j, 7c, and m in communication with the exterior annular openings, n, 0,19, q,

fr and s,see Figs. 2 and 19, the latter being an lenlarged cross section of the-sleeveD2.

in communication with the interiors of the steam holding vessels B and C through the medium of the apertures a and b', and that IOO and qjare united by the channel d.

the openings n ands are connected by the channel c; and,further, 'that the openingsp The channels c and d have branch channels e and f leading to the outer face g of the valve chamber D, which face is flat.

G is a steam chest bolted to the face g', and having a cylindrical valve chamber h with its ports z",j, lc', and Z, leadinginto annular spaces m', n', o', and p. The space m opens into the branch channel f', and the space o into the branch channel e. 6. Within the valve chamber h is a piston valve H having two parts thereof, q and r',

reduced in diameter so that certain of the ports fi,j, 7a', and l may be made to communicate as and for a purpose hereinafter described. Opposite the annular spaces n and 1o', and in communication with them, are (Fig.

6) hollow bosses s and t', and these are respectively connectedwith the hollow bosses a and b by pipes I and J.

K K are cylindrical mercury-holding pots which stand on raised seats u in the steam holding vessels B and C.- Fig. 2.

MkMrepresent annular plates which constitute the lids of the steam holding vessels B and C. These plates are each held tightly in contact with the edge of its steam h olding'vessel by a threaded ring N having-an inner peripheral lip 'n' which rests in a rabbet in the lid.

O O (Figs. 16, 17 and 18) are inner mercury reservoirs, one for each steam holding. vessel, fitting loosely in central apertures in the lids M, and extending downward into the pots K. These reservoirs have exterior lianges a2 and bottoms b2, and into their upper ends, which extend above thelids M, are screwed the plugs c2. Fig. 16 is a vertical section of one of these mercury reservoirs, and Figs. 17 and 18 are, respectively, an under side, and a top view of the same.

The Y mercury reservoirs O are secured against upward movement by danges d2 which rest in circular depressions in the under side of the lids.

P P (Figs. 7,8 and 9) are circular plate valves each having a central cylindrical projection e2 which passes loosely through a hole in the bottom b2 of its reservoir t). The said plate valves have each two horizontal channels f2 y extending from their circumferences to near the central cylindrical projections e2, and also ports g2 and h?, leading from said channels f2 to the upper faces of said valves which are in contact with the bottoms of the reservoirs O. The adjoining faces of the plate valves and reservoirs are true and form tight joints.

Figs. 7, 8 and 9 are respectively, a central cross section, an exterior edge, and a top viewA vof one of the plate valves.

The plate valves P P are threaded, and screwed into the vertical flanges i2 of the cylindrical blocks Q, (Figs. 10, l1 and 12;) and between the blocks and the plate valves See Figs. 5 and l are clamped thin spring-tempered steel dia-v phragms R, Fig.`2. l

Figs. l0, 11 and 12 are respectively an exterior side, a top and an under side View of one of the blocks Q. The horizontal chan-.

phragm R. `By means of the threaded spin dles and their needles the effective size ofthe apertures j? may be regulated.

The object in grooving the spindles S,as shown in Fig. 22 which is a top viewof one of them, is to form passages between the spaces above the diaphragms R andthe interiors ot' the reservoirs O. The adjustment of the needle points in the apertures j? of. the said diaphragms is effected by means of a screw driver, the fiat point of which is inserted in a cnt in the upper endof the spindles S.

In the steam holding vesselB, the lower face of the plate valve Pand the upper face of the cylindrical block Q, are dished in the center (Fig. 2) in order that a large portion of its diaphragm Rinay be exposed, and togive the necessary room for the diaphragm tobulge upward without striking the said platevalve.

This diaphragm is allowed to bulge so that as the pressure of mercury under it increases, it

will pass to a higher and larger part of the needle and thus decrease the effective size of the aperture y2. Vhere the range of -pressures is great, as say from two pounds to eighty, a holeof sufficient size to allow the mercury to pass at the lowest pressure would or might be too large to limit the discharge so that the colored liquid column would not be contained in the most convenient length of measuringv glass tube. In other words, an aperture which would allow the colored column to ascend to near the top of the glass measuring tube with eighty pounds pressure exerted for the space of one minute would be too small to allow any mercury to pass through at the extreme low pressure of two pounds. With the bulging diaphragm as described the effective size of the aperture alters with the pressure on the mercury tending to force it through the aperture. Y

n In the steam holding vessel C, the dia. phragm R is not intended tobulge; and the dishing of the faces of the plate valve and the. cylindrical block, is therefore dispensed with,

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theV said diaphragm being clamped throughl out its entire surface or nearly-so. Each of the interior of the cylindrical pot K, which surrounds it. The blocks Q are prevented from turning circumferentially by means of two ears Q2 the upper ends of which rest between lugs Q3 on the under side of the covering lids M of the steam holding vessels B and C.

U U are spiral springs situated in annular grooves m2 in the blocks Q; and, as they bear against or rest on the bottoms of the pots K, they keep the plate valves P tightly against the faces of the reservoirs O, and also retain the flanges d2 closely in contact with the recessed portions of the lids M,-so as to form steam tightV joints.

The plugs c2 are bored out (Fig. 16) toform packing boxes Ainto which measuring glass tubes V are inserted. The packing isheld in place by the glands n2.

A A (Fig. 2) are tubular protection-cas` ings for the glass tubes V. They are fitted tightlyaround the plugs c2 and are closed at their upper ends by ornamental caps B', which are bored out and provided with soft washers serving to make dust proof joints. The protection casingsare cut away at one side to expose the measuring tubes, as shown in Figs. 2 and 3. The bottoms of the ornamental caps are perforated, and the holes lead into the tubular protection casings for a purpose hereinafter described.

Byreferring to Figs. 16 and 17 it will be seen that in the bottoms and the exterior -anges of the reservoirs O, are ports o2 and p2.

voir and pot K of each steam holding vessel in full communication. The registration of the ports,as described, is effected by means of handles C', secured to the portions of the reservoirs which project above the steam holding vessels B and C. See Figs. 2 and 4.. Stops q2 and r2 on the lids M limit the circumferential movement of the handles C and the reservoirs to which they are fastened. When thehandles are brought together and come in contact with the stops r2, the ports o2 and p2 register with the ports g2 and 71,2, and the plate valves P then offer no obstruction to the passage of the contents of the reservoirs to the pots, or vice versa. But when the said ports are thrown out of register, by the handles being turned toward the stops q2, all avenues of communication between the reservoirs and pots are cut off, except the aperturesj2 in the diaphragms R and the holes 7a2 in the cylindrical blocks Q. The holes 708 are merely supply channels to bring the under side of the perforated diaphragms in communication with the interior of the pots, and may be of any suitable size.

D (Figs. 2 and 3) is a curved rocker adapted to vibrate on a stud s2, projecting backwaid from .the frame A. The ends of this rocker have screws t2 adapted as adjustable tappets The lower. roller d3 hasa fixed position with reference to the tail piece b3 of the rocker D', its spindle c3 being in a circular hole in which it turns freely, but the spindle f3 of the upper and plain roller is confined in a slot g3 in order that the roller may have some vertical adjustment. Springs 713 attached to the tail piece bear onthe two ends of the spindle fs of the plain vertically adjustable roller c3, which ends are slightly grooved for their reception, the springs tending to force the Vupper roller toward the lower one.

E" (Figs. 1, 2, 3 and 4) is a rod whichleads from some part of the engine having a movement in common withthat of the piston. By reference to Fig. 1, it wil-l be seen that the cross-head of the engine has an arm F', temporarily or permanently bolted to it, and this arm, which is provided with a pin 3, is bent so as to bring the pin 713 directly in alignment with the space between the rollers c3and d3. The rod E has a hook js whereby it is connected to the pin Q13, of the arm- F', and it therefore movesin unison with the crosshead.

The rod E is forced tightly into the groove of the lower roller by the resilient action of the springs 713.

G is a spring-supported bar hinged tothe frame A at 7c3, and having two lugs m3 between which the end of the tail piece rests. The said lugs have screws n3 which are so adjusted as to hold the tail piece firmly but nottightly in a vertical position, and the re- Versing valve E in a central one, when the bar Gr is at its highest point. But the extreme end of the tail piece is somewhat reduced in width, and when the bar is lowered or depressed so as to bring the ends of the screws 'n.3 opposite the narrow part, it, the tail piece, is susceptible of a slight swinging motion, but this motion is sufficient to effect a complete forward and backward stroke of the reversing valve E.

H is a knob whereby the bar G may be depressed by hand, to allow of the movement of the rocker and eect the reciprocating stroke of the reversing valve. When the bar G is depressed and the engine piston begins its stroke, the rod E moves the rocker until the tail piece b3 comes in contact with one of the screws n3, when all further motion in that direction is prevented, and the rod E merely passes on. The movement effected by the friction between the rod E and the rollers is, however, sufficient to move the reversing valve E and admit steam from the operative side of the piston to the interior of the steam holding vessel B, while the steam from the back of the piston, or that which retards its stroke, is brought in communication with the interior of the steam holding vessel C.

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At the beginning of the return stroke-lof the engine piston, the rod E reverses the position of the reversing valve E, and the forward steam from the other side of the engine piston is conducted to the vessel B and the back pressure steam to the vessel C. The motion of the reversing valve E is accomplished when the engine piston has moved on its stroke the distance of about one thirtysecond part of an inch, and, during theremainder of the stroke of the engine piston, the rod E is inoperative except that it serves to keep the said reversing valve in the posi` tion in which it has been forced, `until the beginning of the reverse stroke of the engine piston.

The steam valve H (Fig. 5) has an operating stem l with a.knob o3 at the top, and the length of the stemis such vthat the knob is situated immediately under the handles C when they are brought together. Figs. 3 and 4. By this arrangement, the knob o3 is not easily reached or touched except when the handles C are separated; and this interference of therparts is availed of to prevent the steam Valve being opened except when such opening can do no harm, as will hereinafter appear.

. JA (Fig. 5) is a guiding stem leading from the bottom of the steam valve H down through a lug p3 extending from the face of the frame A.

K is a spiral spring coiled about the stem J and confined endwise between the lug p3 and a cupped collar Q3, to retain the steam valve yieldingly in its highest position, or that in which steam is cut olf from the channels c and d which constitute the means of access to the ports of the reversing valve E.

s The downward movement of the steam valve H is limited by a collar r3 whichcomes in contact with the top of the steam chest. In order that in the depression of the steam valve H the bar Gr may also be depressed, and the rocker D thereby released so that the reversing valve E shall becomeoperative, the said b ar is provided with a lateral projection s3 with which the edge of the cupped collar g3 comes in contact in its downward motion. Figs. 3 and 4.

L (Figs. 2 and 3) is a circumferentially toothed dial secured to a flanged sleeve t3 adapted to turn looselyupon a tiXed stud n3 projecting rearward from the frame A.

M and N are pallet arms extending from the hub piece a4 which is passed over'and attached rigidly to a reduced portion at the end of the hub of the rocker D. These pallet arms have spring steel pallets N2 of the shape usually employed in escapements of clock movements, which engage with the teeth of the dial L. The pallets and the teeth'of the dial L form the escapement, which in the oscillation of the rocker D allows the dial to rotate one tooth for each double stroke of the engine piston. (Fig. 15) is confined in a circular box d4 rig- An ordinaryv clock spring O idly attached to the stationary stud as, with its ends connected to pins on the stud and the` toothed dial. TheA spring Ois wound by turning the dial L in the direction opposite to thatin which it is intendedtomov'e inthe operation of the instrument, the palletsbeing formed of springs, as befoiestated, allowing of this winding operation.

P is a pointer fastened to 'the top of the stationary spring box di* with its end bent over the toothed dial/L', Figs. 2,' 3 and4.

The tubular protection casings A 2) Yare each provided with a scale plate e4, which is marked to indicate the p ressure figures obtained in accordance with the theory and operation hereinbefore stated, and the teeth of the dial L are numberedasshown. Figs. 2O and 2l show the scale plates marked as described. The scale plates e4 are forced forlward and held against curved finishing pieces f4 by means of springs g4, one of which is shown in Fig. 2; and a slight vertical adjustment of each scale plate is obtained bymeans of a rack h4 and a pinion i4.

To prepare the instrument for use after the scale plates have been marked, the handles C are both moved in, or'toward each other, until they strike the inner stops. Fig. 4. By this movement ofthe handles, the ports o2 and p2 are opened or brought to register with the ports g2 and, h2. The rcaps B are `then removed, and mercury is poured into the glass tubes until it rises in the pots K and `the inner reservoirs O,'to the dotted line z.

In the charging of the instrument, the mercury will pass around the blocks Q andthe spiral springs U, flow up through the holes k2 and come in contact with `the under side of the diaphragms R. 4A lighter liquid, such as water or water Vand glycerine, suitably colored, is now poured down the glass tubes onto the mercury in the reservoirs O until it rises tothe-,zero point on the scale plates. The ycaps B are then replaced.V When a pot K with its reservoir and measuring glass tube is thus charged,any depression of mercuryin the pot causes arise in the glass tube, and as the area of the surface of mercury in the pot exterior of the reservoir is many'times greater than the transverse area of the liquid column in the glass tube, a very slight fall of mercury will cause a very considerablek rise of the colored liquid in the glass tube.

The rod E which for the sake of convenience and to admit of its adaptation to engines of various sizes is in sections screwed together, is now connected to the armF' rig- .idly attached to the engine cross'head, and the toothed dial turned around until the zero point is directly under the end of the pointer P. The instrument is now ready for use.

Supposing the engine to be in operation,the rod E is at first inoperative, the tail piece b3 being firmly h eld by the screws n3 in thelugs m3 of the Vbar G, andthe rod merely moves forward and backward without communicating any movement to the rocker D. At this IOD IIO

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time the ports j and Zof the steam chest are closed bythe valve H, (see Fig. 5,) and no steam passingthrough thepipes @and Lhollow bosses a and b, and pipes I and J to the steam chest G, can therefore pass through said ports. The operator now takes his watch in hand, and, at the beginning of a minute, presses down the knob o3 which opens the ports jand Z', and places the forward end of the steam cylinder in communication with the exterior of the reversing valve E by the way of the port j, annular space around the reduced part q of the piston valve H, the port i', lthe space m', branch channel f and channel d.'

The other or back end of the steam engine cylinder is placed in communication with the exterior of the said reversing valve E through the portV Z', the annular space around the reduced portion r of the piston valve H, the port 7c', the space o', the branch channel e and the channel c. The depression of the valve H also liberates the tail piece of the rocker D', as before described. Now supposing the engine piston t`o be at the beginning of the forward stroke, and about to move in the direction indicated by the arrow in Fig. 1, the rod E which moves in unison with the engine piston, during the first one thirty-second part of an inch of its stroke, pushes over the tail piece b3 until it strikes' one of the screws n3 in alug mof the springsupported bar G. In this movement, the revel-sing valve E is thrown in the direction indicated by the arrow in Fig. 2, which opens the port g and places the interior of the steam holding vessel B in communication with the channel c', to which forward orahead steam from the back end of the steam cylinder,'and behind the piston, has been admitted, as before described, by the way of the annular opening n, the recess if in the reversing valve E, the port h, the annular opening 0, and the aperture d. At the same time, the portj is opened, and the interior of the steam holding vessel C is brought in communication with the channel d which receives any back pressure or retarding steam that may be acting against the piston, as before de-` scribed, by the way of the annular opening q, the recess u in the reversing valve E, the port 7c, the annular opening r and the aperture b. From the foregoing description it will be seen that the mercury in the steam holding vessel B is now subjected tothe forward or ahead steam, and the mercury in the steam holding vessel C to the back pressure or retarding steam, and this condition of fthings continues until the piston has comaperture j? By the increase in volume of mercury in the reservoirs, the light liquid (water and glycerine) standing thereon is forced up the glass tubes. At the beginning of the return stroke, the reversing valve is reversed in position, and the ports t' and m are opened, which brings the interior of the steam holding vessel B in communication with the channel d which then contains forward or ahead steam from the forward end of the steam engine cylinder, and theinterior of the steam holding vessel C is brought in communication with the channel c which then contains back pressure or retarding steam from the back end of the steam engine cylinder. From this it will be understood that no matter in which direction the engine piston moves, the steam holding vessel B always receives the forward or ahead steam, and the other vessel C, the back pressure or retarding steam. At the completion of the minute, the operator releases the knob 03 which stops the operation of the instrument, and he then notes the heights of the two columns of coloredv liquid as indicated by the gures on the scale plates. The figures indicati'ngthe back pressure must now be deducted from those indicating the ahead or forward pressure, and the remainder is the mean effective pressure to which the piston has been subjected during the minute. During the displacement of the mercury and the rise of the colored liquid columns, the toothed dial L has been turning with an intermittent movement, the distance of one tooth for each double stroke of the engine piston, or complete revolution of the engine, and when the movement of the instrument is stopped, the pointer P will indicate the number of double strokes or complete revolutions made by the engine during the minute. From the data furnished in tigures, as described, the area of the engine piston in inches, and the distance traveled by the piston in feet during each double stroke, being known, the average horse power developed by the engine during the minute may be ascertained by the well known rule used in such cases. The operation of ascertaining the power of the engine being ended, the liquid'columns are 'allowed to fall by turning the plate valves P by means of the handles C', and after the handles are replaced or moved to their original position, the instrument is again ready for use. In turning the handles so as to allow the liquid columns to recede, they are brought over the knob 03 and thereby prevent, or renderdifficult, the opening of the steam valve, which should not be opened until the ports o2, and p2,are closed or brought out of register with the others g2 and h2.

To let oit any steam left inclosed in the vessels B and C at the end of the indicating operation and which would prevent or retard the communicating bodies of mercury coming to a common level, the lids are each provided with a small holem4 which,as the han- IIO dles areturned inward, registers with another hole 'n4 in the flange of each of the reservoirs See Figs. l4C and 18.'

In ascertaining the horse power ot' a condensing engine, the back pressure column is lowered instead of raised, by reason ofthe existence of a partial vacuum on the back of the engine piston, and in computing the effective pressure on the piston, the number registered by this column must be added to, instead of subtracted from, the other, as will be readily understood.

The reason forhavingthezero points adjustable by means of rack and pinion, as described, is to obviate the necessity of great accuracy in pouring in the colored liquid in the glass tubes and also to provide for any evaporation of the said liquid when the instrument has been in .use for a great lengthoi` time.

I claim as my inventionl. The method of ascertaining the average pressure of steam in an engine cylinder, herein described, which consists in subjecting a body of mercury in a vessel having a limited discharge aperture of known capacity, to the same steam pressure, and measuring the mercury discharged, substantially as specified.

2. The method of arriving at the average of a varying pressure of steam acting on a moving engine piston during a given period of time, herein described, which consists in subjecting a body of mercury in a vessel having a limited discharge aperture, to steam in communication with that aecting the said piston, and comparing the quantity of mercury discharged from the said vessel with another quantity discharged through the isame or a similar aperture under a constant pressure, for the same, or a certain proportion of the same, period of time, substantially as specified. Y

3. In a power measuring instrument, the combination of a mercury holding vessel having a limited discharge opening, a pipe to convey steam to the surface of the contained mercury, and a measuring vessel to ascertain the volume of the discharged mercury, substantially as specified.

4. In a power measuring instrument, the combination of a' mercury holding vessel having a limited discharge aperture, a measuring vessel to ascertain the volume of the discharged mercury, a pipe whereby pressure is applied to the surface of the contained mercury, and valve mechanism to control the said applied pressure, substantially as speciied.

5. In a pressure measuring instrument, the combination of a mercury holding vessel having a limited discharge aperture, a measuring vessel to ascertain the volume of the discharged mercury, a pipe leading from the space in the mercury-holding vessel above the contained mercury to one end of an engine cylinder, a second 4pipe leading from the said space above the mercury to the other end of the said engine cylinder, and valve mechanism whereby the said vessel may be placed alternately in communication with each end of the said steam cylinder, substantially as specified.

6. In a pressure measuring instrument, the combination of a mercury holding vessel having a limited discharge, a measuring vessel to 7. In a pressure measuring instrument, the

combination of two mercury holding vessels,

each one of which is provided with a limited discharge and with a measuring vessel to ascertain the volume of the discharged mercury, a pipe leading from above the surface of the mercury in the two vessels to one end `of an engine cylinder, a second pipe leading 4from the same place to the other end of the isaid engine cylinder, and valve mechanism jactuated primarily from the piston of the engine whereby, in the operation of the engine,

the forward steam from each end ot' the steam Icylinder is alternately admitted to one mercury holding vessel, and the back pressure :steam from each end of the steam cylinder to :the other mercury holding vessel, substantially as specicd.

8. In an instrument for ascertaining the Lpower of a steam engine, devices for registering the mean etfective pressure of steam acting on the engine piston for a certain period of time, and devices for registering the revolutions of the engine for the same period of time, combined with mechanism whereby the two sets of devices are simultaneously placed in operation, substantially as specified.

9. In a pressure measuring instrument, consisting primarily of a mercury holding Vessel having a limited discharge leading to a measuring vessel, a valve which controls the action of steam from the cylinder of a steam engine on the surface of the contained mercury,

and actuating Lmechanism for the said-valve having a limited movement less than the stroke of the engine piston, combined with a device operated by the engine piston and having a movement in unison therewith, which device is connected with the said valve actuating mechanism and imparts onlya portion IOO of its movement thereto, whereby the said f controlling valve is operated at the beginning of each single stroke of the piston, and then held in its position until the completion of the said single stroke substantially as specitied.

10. In a pressure measuring instrument, the

combination of a valve, avalve-operating pivoted rocker with a vibratory tail piece, a rod connected with some part of an engine having a movementin unison with the engine pist0n, the free end of which rod passes through the vibratory tail piece, and friction producing devices or rollers forming a part of the tail piece to clamp the said rod and serve to communicate the first part of its motion to the said valve-operating rocker, substantially as specified.

11. In apressure measuringinstrument, the combination of a steam holding vessel containing mercury, and a mercury reservoir inserted in the said steam holding vessel with its end, which is immersed in the mercury, provided with a small aperture, whereby, as pressure is applied to the surface of the mercury exteriorly of the reservoir, .'he mercury is made to rise in the said reservoir, substan-` tially as specified.

I2. In apressure measuring instrument, the combination of a steam holding vessel containing mercury, a mercury holding vessel having at its lower end a valve which may be opened and closed, and also a diaphragm having asmall aperture which is at all times open, the said aperture forming a constant means of communication between the mercury holding portion of the steam holding vessel, and the interior of the reservoir, substantially as specified.

13. In a pressure measuringinstrument, the combination of a steam-.holding vessel containing mercury, a mercury holding reservoir having at its lower end a ported plate valve which isimmersed in the mercury, and also a diaphragm secured to the plate valve having a small\ aperture which is never closed and forms a means of communication between the steam holding vessel and the interior of the reservoir, substantially as specified.

I4. In apressure measuring instrument, the combination of a steam holding vessel in which-is inserted la reservoir having a con-- trollable opening and a non-controllable aperture, both of which serve as means of communication between the steam-holding vessel and the reservoir, and a measuring tube'leading from the upper end of the said reservoir, substantially asspecified.

l5. A power measuring instrument, which consists of a steam holding vessel having an apertured reservoir in communication with the said vessel, valve mechanism whereby the admission of steam to the said vessel is controlled, and means whereby a motion in unison with the engine piston is communicated t0 the valve mechanism, combined with a dial and an escapementwhereby, at each complete stroke of the engine, the dial is allowed or `made to perform apart of a revolution, substantially as specified.

16. In a power measuringinstrument, a reversin g valve, substantially as described, combined with an actuating pivoted rocker having a tail piece with friction rollers therein, a rod leading from some part of an engine having a movement in common With the engine piston, which is clamped between the friction rollers, and a holding and releasing bar where- 'stantially as specied.

WILLIAM THOMPSON HOWARD. Witnesses: v

EDWIN CRUsE, J. M. POND.

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